Apparatus and method for formation of foil-shaped stent struts

ABSTRACT

A device and method is disclosed for reducing turbulent blood flow over stent struts of an intravascular stent implanted in, for example, a coronary artery. An abrasive slurry is passed over the struts of an intravascular stent in order to remove a portion of the stent struts to form an airfoil shape. When the stent having airfoil-shaped struts is implanted in an artery, the flow of blood over the airfoil shape will reduce the likelihood of turbulent blood flow and thereby will reduce the likelihood of turbulent blood flow and thereby reduce the likelihood of a buildup in plaque or injury to the vessel wall.

BACKGROUND

The invention relates generally to providing an apparatus for using an abrasive slurry for the removal of metal on products made from metals. More particularly, the invention relates to an apparatus for and method of using an abrasive slurry on medical devices made of titanium, stainless steel, tungsten, nickel-titanium, tantalum, cobalt-chromium-tungsten, cobalt-chromium, and the like to form a more hemodynamically compatible device.

While a wide range of products or devices can be made from the listed metal alloys for use with the present invention, medical devices are particularly suitable due to the biocompatible characteristics of these alloys. Thus, for example, implantable medical devices or devices that are used within the human body are particularly suitable and can be made from these alloys that have been treated in accordance with the present invention. More particularly, and as described in more detail herein, intravascular stents can be made from the listed alloys that have been treated according to the invention. Thus, while the description of prior art devices and of the invention herein refers mainly to intravascular stents, the invention is not so limited to medical products or intravascular stents.

Stents are generally metallic tube shaped intravascular devices which are placed within a blood vessel to structurally hold open the vessel. The device can be used to maintain the patency of a blood vessel immediately after intravascular treatments and can be used to reduce the likelihood of development of restenosis. Expandable stents are frequently used as they may travel in compressed form to the stenotic site generally either crimped onto an inflation balloon or compressed into a containment sheath in a known manner.

Metal stents can be formed in a variety of expandable configurations such as helically wound wire stents, wire mesh stents, weaved wire stents, metallic serpentine stents, or in the form of a chain of corrugated rings. Expandable stents, such as wire mesh, serpentine, and corrugated ring designs, for example, do not possess uniformly solid tubular walls. Although generally cylindrical in overall shape, the walls of such stents are perforated often in a framework design of wire-like elements or struts connected together or in a weave design of cross threaded wire.

Expandable stents formed from metal offer a number of advantages and are widely used. Metallic serpentine stents, for example, not only provide strength and rigidity once implanted they also are designed sufficiently compressible and flexible for traveling through the tortuous pathways of the vessel route prior to arrival at the stenotic site. Additionally, metallic stents may be radiopaque, thus easily visible by radiation illumination techniques such as x-ray film.

It is highly desirable for the surface of the stent to be extremely smooth so that it can be inserted easily and experience low-friction travel through the tortuous vessel pathway prior to implantation. A roughened outer surface may result in increased frictional obstruction during insertion and excess drag during travel to the stenotic site as well as damaging the endothelium lining of the vessel wall. A rough surface may cause frictional resistance to such an extent as to prevent travel to desired distal locations. A rough finish may also cause damage to the underlying inflation balloon. A less rough finish decreases thrombogenicity and increases corrosion resistance.

Stents have been formed from various metals including stainless steel, tantalum, titanium, tungsten, nickel-titanium which is commonly called Nitinol, and alloys formed with cobalt and chromium. Stainless steel has been extensively used to form stents and has often been the material of choice for stent construction. Stainless steel is corrosion resistant, strong, yet may be cut into very thin-walled stent patterns.

Cobalt-chromium alloy is a metal that has proven advantages when used in stent applications. Stents made from a cobalt-chromium alloy may be thinner and lighter in weight than stents made from other metallic materials, including stainless steel. Cobalt-chromium alloy is also a denser metal than stainless steel. Additionally, cobalt-chromium stents are nontranslucent to certain electromagnetic radiation waves, such as X-rays, and, relative to stainless steel stents, provide a higher degree of radiopacity, thus being easier to identify in the body under fluoroscopy.

Metal stents, however, suffer from a number of disadvantages. They often require processing to eliminate undesirable burrs, nicks, or sharp ends. Expandable metal stents are frequently formed by use of a laser to cut a framework design from a tube of metal. The tubular stent wall is formed into a lattice arrangement consisting of metal struts with gaps therebetween. Laser cutting, however, typically is at high temperature and often leaves debris and slag material attached to the stent. Such material, if left on a stent, would render the stent unacceptable for implantation. Treatment to remove the slag, burrs, and nicks is therefore required to provide a device suitable for use in a body lumen.

Descaling is a first treatment of the surface in preparation for further surface treatment such as electropolishing. Descaling may include, for example, scraping the stent with a diamond file, followed by dipping the stent in a hydrochloric acid or an HCl mixture, and thereafter cleaning the stent ultrasonically. A successfully descaled metal stent should be substantially slag-free in preparation for subsequent electropolishing.

Further finishing is often accomplished by the well known technique of electropolishing. Grinding, vibration, and tumbling techniques are often not suited to be employed on small detailed parts such as stents.

Electropolishing is an electrochemical process by which surface metal is dissolved. Sometimes referred to as “reverse plating,” the electropolishing process actually removes metal from the surface desired to be smoothed. The metal stent is connected to a power supply (the anode) and is immersed in a liquid electrolytic solution along with a metal cathode connected to the negative terminal of the power supply. Current is applied and flows from the stent, causing it to become polarized. The applied current controls the rate at which the metal ions of the anodic stent are generally removed and diffused through the solution to the cathode.

The rate of the electrochemical reaction is proportional to the current density. The positioning and thickness of the cathode in relation to the stent is important to make available an even distribution of current to the desired portion of the stent sought to be smoothed. For example, some prior art devices have a cathode in the form of a flat plate or a triangular or single wire loop configuration, which may not yield a stent or other medical device with a smooth surface on all exposed surfaces. For example, the prior art devices do not always provide a stent having a smooth surface on the inner tubular wall of the stent where blood flow will pass.

Most prior art stents are laser cut from a thin-walled metal tube leaving a mesh framework of stent struts. Typically, the stent struts have a rectangular transverse cross-section. When implanted in an artery, the rectangular-shaped cross-section of the stent struts may produce blood flow turbulence in the artery resulting in adverse vascular reactions such as the proliferation of restenosis.

What is needed is an apparatus and a process for treating a product or device made of a metal alloy to remove metal from the device to thereby reduce the likelihood of turbulent blood flow through the device. The present invention satisfies this need.

SUMMARY OF THE INVENTION

The invention is directed to an improved apparatus and method for the treatment of an intravascular stent formed from a metal alloy. The invention is directed to an apparatus and method for passing an abrasive slurry over the struts of an intravascular stent in order to remove a portion of the stent struts to form an airfoil shape. More particularly, the transverse cross-section of one more struts of the stent have a shape that resembles an airfoil or a hydrofoil which will reduce turbulent blood flow in the vasculature in which the stent is implanted, thereby improving clinical outcome. In one embodiment, a chamber holds a stent stationary while an abrasive slurry flows through the inner lumen of the stent. As the abrasive slurry passes over the stent struts, metal is removed from a first edge and, to a lesser degree, metal is removed from a second edge of the strut. More metal is removed from the first edge than from the second edge, resulting in a cross-sectional shape resembling an airfoil.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 an elevational view, partially in section, of a stent of the present invention mounted on a rapid exchange delivery catheter and positioned within an artery.

FIG. 2 is an elevational view, partially in section, similar to that in FIG. 1, wherein the stent is expanded within the artery, so that the stent embeds partially within the arterial wall.

FIG. 3 is an elevational view, partially in section, showing the expanded stent implanted within the artery after withdrawal of the rapid exchange delivery catheter.

FIG. 4 is a cross-sectional view of a prior art stent in which the stent struts have a rectangular cross-section thereby causing turbulent flow of blood through the artery.

FIG. 5 is a plan view of a flattened stent of one embodiment of the invention which illustrates a pattern of rings and links.

FIG. 6 is a partial plan view of the stent of FIG. 5 which has been expanded to approximately 4.0 mm inside diameter.

FIG. 7 is a cross-sectional view taken along lines 7-7 depicting a rectangular cross-section of a stent strut of FIG. 6.

FIG. 8 is an elevational view, partially in section, of a chamber assembly for pumping an abrasive slurry through the inner diameter of the stent to remove metal from the stent struts.

FIG. 9 is a perspective view of the chamber assembly of FIG. 8.

FIG. 10 is a partial cross-sectional view of the chamber assembly of FIG. 8 depicting the stent removably mounted in the chamber.

FIGS. 11A-11D are a series of cross-sectional views of a single strut of the stent of the invention as the abrasive slurry passes over the stent and progressively removes metal from the stent strut.

FIG. 12 is a transverse cross-sectional view airfoil-shaped stent strut partially embedded in an artery wall.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention stent improves on existing stents by providing a longitudinally flexible stent having a uniquely designed pattern and novel interconnecting members. In addition to providing longitudinal flexibility, the stent of the present invention also provides radial rigidity and a high degree of scaffolding of a vessel wall, such as a coronary artery. The present invention stent is processed so that it is more hemodynamically compatible and causes less blood flow turbulence when implanted in an artery.

Turning to the drawings, FIG. 1 depicts a prior art stent 10 mounted on a conventional catheter assembly 12 which is used to deliver the stent and implant it in a body lumen, such as a coronary artery, peripheral artery, or other vessel or lumen within the body. The catheter assembly includes a catheter shaft 13 which has a proximal end 14 and a distal end 16. The catheter assembly is configured to advance through the patient's vascular system by advancing over a guide wire by any of the well known methods of an over the wire system (not shown) or a well known rapid exchange catheter system, such as the one shown in FIG. 1.

Catheter assembly 12 as depicted in FIG. 1 is of the well known rapid exchange type (RX) which includes an RX port 20 where the guide wire 18 will exit the catheter. The distal end of the guide wire 18 exits the catheter distal end 16 so that the catheter advances along the guide wire on a section of the catheter between the RX port 20 and the catheter distal end 16. As is known in the art, the guide wire lumen which receives the guide wire is sized for receiving various diameter guide wires to suit a particular application. The stent is mounted on the expandable member 22 (balloon) and is crimped tightly thereon so that the stent and expandable member present a low profile diameter for delivery through the arteries.

As shown in FIG. 1, a partial cross-section of an artery 24 is shown with a small amount of plaque that has been previously treated by an angioplasty or other repair procedure. Stent 10 is used to repair a diseased or damaged arterial wall which may include the plaque 26 as shown in FIG. 1, or a dissection, or a flap which are sometimes found in the coronary arteries, peripheral arteries and other vessels.

In a typical procedure to implant stent 10, the guide wire 18 is advanced through the patient's vascular system by well known methods so that the distal end of the guide wire is advanced past the plaque or diseased area 26. Prior to implanting the stent, the cardiologist may wish to perform an angioplasty procedure or other procedure (i.e., atherectomy) in order to open the vessel and remodel the diseased area. Thereafter, the stent delivery catheter assembly 12 is advanced over the guide wire so that the stent is positioned in the target area. The expandable member or balloon 22 is inflated by well known means so that it expands radially outwardly and in turn expands the stent radially outwardly until the stent is apposed to the vessel wall. The expandable member is then deflated and the catheter withdrawn from the patient's vascular system. The guide wire typically is left in the lumen for post-dilatation procedures, if any, and subsequently is withdrawn from the patient's vascular system. As depicted in FIGS. 2 and 3, the balloon is fully inflated with the stent expanded and pressed against the vessel wall, and in FIG. 3, the implanted stent remains in the vessel after the balloon has been deflated and the catheter assembly and guide wire have been withdrawn from the patient.

The stent 10 serves to hold open the artery after the catheter is withdrawn, as illustrated by FIG. 3. Due to the formation of the stent from an elongated tubular member, the undulating components of the stent are generally rectangular in transverse cross-section. When the stent is expanded, it is pressed into the wall of the artery, however, portions of the rectangular cross-section may protrude into the artery lumen and may interfere with the blood flow through the artery. The stent is pressed into the wall of the artery and will eventually be covered with endothelial cell growth which will minimize blood flow interference. The undulating portion of the stent provides good tacking characteristics to prevent stent movement within the artery. Furthermore, the closely spaced cylindrical elements at regular intervals provide uniform support for the wall of the artery.

Referring to FIG. 4, a portion of an artery 24 is shown in cross-section with a typical prior art stent at least partially embedded in the artery wall. The stent is comprised of rectangular-shaped stent struts 27 that have an inner surface 28 that faces the blood flow. In FIG. 4, the blood is flowing from left to right in the artery. Because of the rectangular-shaped stent struts 27 having a vertical surface impeding blood flow, there is some turbulent blood flow in and around the stent struts as shown by the diagrammatic arrows in FIG. 4. These localized areas of turbulent blood flow produce adverse vascular reactions such as the proliferation of restenosis and the formation of plaque 26. Typically, the rectangular-shaped stent struts 27 will have rounded corners due to electropolishing, however, even though the corners have been rounded there is still turbulent blood flow that may produce the adverse vascular reactions.

Referring to FIG. 5, stent 30 is shown in a flattened condition so that the pattern can be clearly viewed, even though the stent is in a cylindrical form in use. The stent is typically formed from a tubular member.

As shown in FIGS. 5-6, stent 30 is made up of a plurality of cylindrical rings 40 which extend circumferentially around the stent when it is in a tubular form (see FIG. 3). Each cylindrical ring 40 has a cylindrical ring proximal end 46 and a cylindrical ring distal end 48. Typically, since the stent is laser cut from a tube there are no discreet parts such as the described cylindrical rings and links. However, it is beneficial for identification and reference to various parts to refer to the cylindrical rings and links and other parts of the stent as follows.

Each cylindrical ring 40 defines a cylindrical plane 50 which is a plane defined by the proximal and distal ends 46,48 of the ring and the circumferential extent as the cylindrical ring travels around the cylinder. Each cylindrical ring includes cylindrical outer wall surface 52 which defines the outermost surface of the stent, and cylindrical inner wall surface 53 which defines the innermost surface of the stent. Cylindrical plane 50 follows the cylindrical outer wall surface.

An undulating link 54 is positioned within cylindrical plane 50. The undulating links connect one cylindrical ring 40 to an adjacent cylindrical ring 40 and contribute to the overall longitudinal flexibility to the stent due to their unique construction. The flexibility of the undulating links derives in part from curved portion 56 connected to straight portions 58 wherein the straight portions are substantially perpendicular to the longitudinal axis of the stent. Thus, as the stent is being delivered through a tortuous vessel, such as a coronary artery, the curved portions 56 and straight portions 58 of the undulating links will permit the stent to flex in the longitudinal direction which substantially enhances delivery of the stent to the target site. The number of bends and straight portions in a link can be increased or decreased from that shown, to achieve differing flexibility constructions. With the straight portions being substantially perpendicular to the stent longitudinal axis, the undulating link acts much like a hinge at the curved portion to provide flexibility. A straight link that is parallel to the stent axis typically is not flexible and does not add to the flexibility of the stent.

Referring to FIGS. 5-6, the stent 30 can be described more particularly as having a plurality of first peaks 60, second peaks 61, and valleys 62. Although the stent is not divided into separate elements, for ease of discussion references to peaks and valleys is appropriate. The number of peaks and valleys can vary in number for each ring depending upon the application. Thus, for example, if the stent is to be implanted in a coronary artery, a lesser number of peaks and valleys are required than if the stent is implanted in a peripheral artery, which has a larger diameter than a coronary artery. As can be seen for example in FIG. 6, peaks 60,61 are in phase 63, meaning that the peaks 60,61 point in the same direction and are substantially aligned along the longitudinal axis of the stent. It may be desirable under certain circumstances to position the peaks so that they are out of phase (not shown), that is, the peaks of one ring would be circumferentially offset from the peaks of an adjacent ring so that the apex of adjacent peaks pointed toward each other. As shown in FIGS. 5-6, the peaks are circumferentially offset 64 from the valleys and from the undulating link 54. Positioning the peaks, valleys, and undulating links in this manner, provides a stent having uniform expansion capabilities, high radial strength, a high degree of flexibility, and sufficient wall coverage to support the vessel.

As shown in FIG. 7, a rectangular-shaped stent strut 80 is shown in a transverse cross-sectional configuration from one of the peaks 69 from FIG. 6. More specifically, during a typical laser cutting of a thin metallic tube, the resulting transverse cross-sectional shape of all of the stent struts are generally a rectangular-shaped stent strut 80 like that shown in FIG. 7. Further processing including electropolishing will remove the sharp corners so that the basic overall rectangular shape remains, only with rounded corners so as to have a less invasive impact on the arterial wall when the stent is delivered and implanted. As previously described with respect to the rectangular-shaped stent struts in FIGS. 4 and 7, such a cross-sectional shape likely will result in turbulent blood flow and the adverse affects resulting therefrom. While FIG. 7 illustrates a rectangular-shaped stent strut, other cross-sectional configurations will benefit from the present invention as well. Thus, for example, a square cross-section, or any other cross-section having a leading edge that will disrupt blood flow, will benefit from the present invention.

As shown in FIGS. 8-11D, the stent of the present invention is placed in a chamber in which an abrasive slurry flows through an inner lumen of the stent in order to remove metal from the stent struts and shape certain of the struts into an airfoil or hydrofoil shape. More specifically, those stent struts that are substantially perpendicular to the longitudinal axis of the stent and thereby the flow of abrasive slurry, will be formed into a cross-sectional shape of an airfoil or a hydrofoil, in which the leading edge of the strut is thicker than the trailing end of the strut. When in use, as blood flows along the strut surface, it will maintain a laminar flow without disturbing the adjacent vasculature as much as if the stent strut were rectangular shaped thereby causing turbulent blood flow. While the stent struts of the present invention may not be a perfect airfoil shape or hydrofoil shape where the trailing edge would be relatively sharp, the trailing edge thickness is reduced compared to the leading edge thickness, but still has sufficient thickness to provide radial strength to hold the stent open and to avoid mechanically scoring or otherwise damaging the tissue of the vessel wall.

In keeping with the invention, as shown in FIGS. 8-10, a chamber 82 has a longitudinal bore 84 extending therethrough and is configured for receiving a stent 30. The diameter of the longitudinal bore is configured to be slightly greater than the outer diameter of the stent 30 so that the stent 30 can be placed in the longitudinal bore without pushing on or having an interference fit that may damage the stent struts. The chamber 82 has an end cap 86 that can be secured to the chamber by any conventional means such as screw threads (not shown) or a ratcheting lock, both of which are known in the art. A longitudinal axis 88 extends through the longitudinal bore 84 of the chamber. The chamber has a first end 90 and a second end 92 defining the overall length of the chamber, which can vary depending upon the length of the stent that is inserted therein.

As shown in FIG. 10, the stent 30 is mounted or inserted into the longitudinal bore 84 and the outer diameter of the stent is just slightly less than the diameter of the longitudinal bore 84. In this embodiment, the stent 30 is held in place in the longitudinal bore by a flange 94 or ridge which will ensure that the stent does not move longitudinally as the abrasive slurry flows past the stent and removes metal. In this embodiment, a second longitudinal bore 96 is formed near the second end 92 of the chamber 82 wherein the second longitudinal bore has a diameter that is less than the outer diameter of the stent and less than the diameter of the longitudinal bore 84.

The longitudinal bore 84 has a diameter that is greater than the outer diameter of the stent 30. It is intended that different sized chamber 82 having different diameter longitudinal bores 84 be used for stents having different outer diameters. For example, a typical coronary artery stent in the manufactured configuration can have an outer diameter from between 2 mm to 3.5 mm, and have a length between 8 mm and 30 mm. More typically, a coronary stent has an outer diameter of 3 mm and length of 20 mm. The longitudinal bore 84 has a diameter that is greater than the outer diameter of the stent so that the stent can be easily inserted into the chamber 82 and into longitudinal bore 84 without scraping or damaging the stent struts. After the stent is inserted into the longitudinal bore 84, the end cap 86 is secured to the chamber 82 so that the end cap abuts one end of the stent 30 but does not force the stent against the flange 94 or ridge which is at the opposite end of the longitudinal bore from the end cap. Thus, after the end cap is secured to the chamber, the stent should have substantially no longitudinal movement within the longitudinal bore 84, and just have a slight amount of clearance between the diameter of the longitudinal bore and the outer diameter of the stent.

In further keeping with the invention, and referring to FIGS. 11A-11D, an abrasive slurry 100 flows over the stent struts 102 of stent 30. The abrasive slurry 100 enters the chamber 82 through aperture 104 in the end cap 86 and flows through the longitudinal bore 84 of the chamber. As can be seen in FIGS. 11A-11D, as the abrasive slurry flows over the stent struts 102, which typically have a rectangular cross-section as shown in FIG. 7, the first edge 106 of the stent strut becomes rounded and metal is removed from the first edge at a greater rate than at the second edge 108. In other words, the first edge 106 of the stent strut 102 is directly in the flow of the abrasive slurry 100 and will wear down by metal being removed from the first edge at a rate faster than metal being removed from the second edge 108 on the downstream side of the abrasive slurry. As the abrasive slurry 100 travels over the stent strut 102, it removes less metal from second edge 108 since that edge is not directly in line with the flow of slurry. Thus, the second edge 108 will have a thickness that is greater than the thickness of first edge 106, and both the first edge and the second edge will be curved, thereby taking the shape of an airfoil or hydrofoil. It is noted that first edge 106 does not have so much metal removed that it resembles a knife edge, like a typical airfoil or hydrofoil, but that some metal is removed so that the first edge 106 has less thickness than the second edge 108, yet the stent strut 102 still has enough cross-sectional area so as to not compromise the structural integrity of the stent. In other words, after processing with the abrasive slurry 100, the stent 30 will still have the structural integrity to hold open a vessel, such as a coronary artery, yet will have the benefit of the stent struts having an airfoil shaped cross-section.

More specifically, the strut radial thickness of stent 30 for a coronary artery stent typically is about 0.0032 inch. It will be appreciated, however, that the strut radial thickness can be thicker or thinner, depending on the stent design and where it is implanted. Thus, the strut radial thickness can be in the range from 0.060 inch to 0.002 inch. The present invention reduction in radial thickness of the struts can range from about 5% to about 20% at the first edge 106 and from about 3% to about 15% at the second edge 108. Preferably, the radial thickness of the first edge 106 is reduced by 20% and radial thickness of the second edge is reduced by 5%. As an example, for a stent strut that has a radial thickness of 0.0032 inch, the first edge 106 will be 20% thinner, or about 0.0026 inch and the second edge 108 will be 5% thinner, or about 0.003 inch. Further, the strut surface extending between the first edge 106 and second edge 108 may be straight or slightly curved and essentially form a taper, gradually getting thicker going from the first edge toward the second edge.

Referring to FIGS. 8-11D, it will be appreciated that those stent struts 102 that will benefit the most from the use of the abrasive slurry 100 in chamber 82 are those stent struts that are perpendicular to the flow of the abrasive slurry. Thus, for example, referring to FIG. 6, peak 69 and straight portions 58 are stent struts that are substantially perpendicular to the longitudinal axis of the stent and thus are perpendicular to the flow of the abrasive slurry 100. It is expected that these stent struts will have a cross-sectional shape that resembles an airfoil or hydrofoil as previously discussed. Those stent struts that are not substantially perpendicular to the direction of the flow of the abrasive slurry 100, also benefit from the present invention in that the transverse cross-section may not have a perfect airfoil-shaped cross-section, however, the first edge 106 of such stent struts will generally have more metal removed than the second edge 108 of such stent struts.

The stent 30 of the present invention can be mounted on a balloon catheter similar to that shown in FIG. 1. The stent is tightly compressed or crimped onto the balloon portion of the catheter and remains tightly crimped onto the balloon during delivery through the patient's vascular system. When the balloon is expanded, the stent expands radially outwardly into contact with the body lumen, for example, a coronary artery. When the balloon portion of the catheter is deflated, the catheter system is withdrawn from the patient and the stent remains implanted in the artery. Similarly, if the stent of the present invention is made from a self-expanding metal alloy, such as nickel-titanium or the like, the stent may be compressed or crimped onto a catheter and a sheath (not shown) is placed over the stent to hold it in place until the stent is ready to be implanted in the patient. Such sheaths are well known in the art. Further, such a self-expanding stent may be compressed or crimped to a delivery diameter and placed within a catheter. Once the stent has been positioned within the artery, it is pushed out of the catheter or the catheter is withdrawn proximally and the stent held in place until it exits the catheter and self-expands into contact with the wall of the artery. Balloon catheters and catheters for delivering self-expanding stents are well known in the art.

It is important to note that the airfoil shape of the stent strut 102 as shown for example in FIG. 11D, has a second edge 108 that is thicker than a first edge 106. When the stent 30 is implanted in a vessel, such as a coronary artery 24 shown in FIG. 12, it is more likely that blood in the artery will flow from the second edge 108 toward the first edge 106 much like the airflow over the airfoil of an airplane wing. In other words, the leading edge (second edge 108) of the stent strut 102 is thicker than the trailing edge (first edge 106), and as blood flows along the strut surface as shown by Arrow A, it maintains a laminer flow without disturbing the adjacent vasculature as much as if the stent strut were more rectangular-shaped. Further, the present invention using the slurry solution forming the stent strut, may also form a stent strut that has a taper shape rather than an airfoil shape, and still be beneficial in the reduction of blood flow turbulence.

While the invention has been illustrated and described herein, in terms of its use as an intravascular stent, it will be apparent to those skilled in the art that the stent can be used in other body lumens. Other modifications and improvements may be made without departing from the scope of the invention. 

1. A method for forming a stent, comprising: providing a metallic stent having a cylindrical shape and a pattern of stent struts; placing the stent in a chamber; injecting an abrasive slurry through the chamber and through a lumen of the stent; removing metal from an inner surface of at least one of the stent struts by the abrasive slurry flowing over the inner surface of the stent.
 2. The method of claim 1, wherein as the abrasive slurry flows over the inner surface of the at least one stent strut, a transverse cross-section of the strut is transformed from a substantially rectangular shape into the shape of an airfoil.
 3. The method of claim 1, wherein the abrasive slurry has a low viscosity so that it flows through the stent lumen without bending the stent struts.
 4. (canceled)
 5. The method of claim 1, wherein the abrasive slurry has a pressure range of 1500 psi to 3500 psi.
 6. The method of claim 1, wherein the abrasive slurry contains abrasive particles having an average particle in the range of 12.0 microns (0.0005 inch) to 6.5 microns (0.0003 inch).
 7. The method of claim 1, wherein the abrasive slurry contains a polymer.
 8. The method of claim 1, wherein the airfoil-shaped cross-section of the at least one stent strut has a first edge that is thinner than a second edge.
 9. The method of claim 7, wherein the at least one stent strut has a curved inner surface that extends between the first edge and the second edge.
 10. The method of claim 7, wherein as the abrasive slurry flows over the inner surface of the at least one stent strut, the slurry flows in a direction from the first edge toward the second edge.
 11. The method of claim 9, wherein the abrasive slurry removes more metal from the first edge than from the second edge.
 12. The method of claim 2, wherein the transverse cross-sectional shape of the at least one stent strut before flowing the abrasive slurry over the inner surface is substantially rectangular with radiused corners.
 13. The method of claim 1, wherein the metal removed from the at least one stent strut reduces the radial thickness of the first edge from about 5% to about 20% and the second edge from about 3% to about 15%.
 14. The method of claim 1, wherein the stent has an outer surface and a radial thickness defined by the outer surface and the inner surface, the radial thickness being in a range of 0.002 inch to 0.060 inch. 